Concerns about the negative effects of microplastics (MPs) on human health have led to increasing attention to the occurrence of MPs in the aquatic environment. Recent studies have focus on the spatio-temporal distribution of MPs in rivers for residential and agricultural areas. Qarasu River Basin, watershed to Gorgan Bay, is the site of many permanent rivers and the levels of MP pollution in those rivers are unknown. This research was conducted in three different types of land use: forest, residential, and agricultural along 8 different rivers. A total of 9 fish species were identified and the presence of MPs in 87% of fish was confirmed. The prevalence of MP among species was Liza sp. > Carassius gibelio > Gambusia holbrooki > Rutilus rutilus > Neogobius melanostomus > Cyprinus carpio = Vimba vimba > Rutilus frisii > Barbus sp. The highest frequency of MPs was observed in Qarasu River (1880 ± 251 n/kg) and Mohammadabad River (184 ± 1340 n/kg) in agricultural land use, and the lowest frequency was related to Baghu and Ziarat Rivers with 660 ± 77 and 600 ± 91 n/kg found in forest land use respectively. The highest type, color, and size of MP sediments were fragment, black, and 1–2 mm, respectively. The highest type, color, and size of MP in fishes were fiber, black, and 0.5–0.1 mm respectively. Overall according to the source tracing result, agricultural land use was the main source of MP pollution of Gorgan Bay. The Bay is strongly affected by the incoming rivers, the Qarasu River Basin as the most important river supplying water.

This report presents investigation performed as a part of a wider study desined to examine the level of pollution effects on fish in Ohrid lake (The Former Yugoslav Republic of Macedonia). Faunal investigation of the fish Barbus meridionalis petenyi Heck. were carried out at the five localities in Ohrid lake. Microscope analysis of histological preparation of barbel hepatic tissue displayed a dominant presence of granulomatous inflammation on a level of hepatocelular parenchyme and cholangiofibrosis on a level of hepatic bile duck. The analysis did not exhibit any correlation between the granulomatous inflammation and the manifestation of the cholangiofibrous alterations.